The Extraordinary Properties
of Water
Water
 A water molecule (H2O), is made up of
three atoms --- one oxygen and two
hydrogen.
 The bonds between the atoms are polar
covalent bonds.
H
O
H
Water is Polar
 The oxygen end has a slight negative
charge
 The hydrogen end has a slight positive
charge
 The positive and negative charges
attract each other.
Water is Polar
 In each water
molecule, the oxygen
atom attracts more
than its "fair share"
of electrons.
 The oxygen atom is
more electronegative
than the hydrogen
atoms.
This symbol indicates electronegativity.
The Oxygen atom has a slight negative charge.
Water is Polar
 This is what causes the water to be
POLAR
 However, water is neutral (equal number
of e- and p+) --- Zero Net Charge
Hydrogen Bonds Exist Between Water Molecules
 Hydrogen bonds are
temporary bonds formed
between a highly
electronegative atom of a
polar molecule and a
Hydrogen atom of another
molecule.
 One hydrogen bond is weak,
but many hydrogen bonds
are strong
Interaction Between Water Molecules
H
O
The negative Oxygen end of one water molecule is
attracted to the positive Hydrogen end of another water
molecule to form a HYDROGEN BOND
Interaction Between Water Molecules
O
Each hydrogen atom in one water molecule forms a single
hydrogen bond with each oxygen atom of another water
molecule.
Interaction Between Water Molecules
Each oxygen atom in one water molecule forms two
hydrogen bonds with two hydrogen atoms from two other
water molecules.
Interaction Between Water Molecules
 As a result, each
water molecule can
form as many as four
hydrogen bonds with
four other water
molecules.
This leads to unique properties of water
that are necessary for life on Earth.
What are
the
Properties
of Water?
Properties of Water
 At sea level, pure water boils at 100 °C and
freezes at 0 °C.
 The boiling temperature of water decreases at
higher elevations (lower atmospheric pressure).
 For this reason, an egg will take longer to boil
at higher altitudes
Properties of Water
Cohesion
Properties of Water
 Cohesion- water molecules stick to each other
 This results in surface tension (a measure of
the strength of water’s surface)
 This in turn produces a surface film that
allows some insects to walk across water.
Cohesion …
Helps insects walk across
water
Properties of Water
Cohesion
Adhesion
Adhesion
• Attraction between two different substances.
• Water will make hydrogen bonds with other
surfaces such as glass, soil, plant tissues, and
cotton.
 Capillary action-water molecules will “tow” each
other along when in a thin glass tube.
 Example: transpiration process which plants
and trees remove water from the soil, and
paper towels soak up water.
Adhesion Causes Capillary Action
Which gives
water the
ability to
“climb”
structures.
Adhesion Also Causes Water to …
Hold onto plant
leaves
Note: the “spheres”
formed in both
photos are the result
of cohesion 
Attach to a
silken spider
web
Properties of Water
Cohesion
Adhesion
High Specific Heat
High Specific Heat
• Specific heat - amount of heat needed to raise
or lower 1g of a substance 1° C.
 Water resists temperature change, both for
heating and cooling.
 Water can absorb or release large amounts of
heat energy with little change in actual
temperature.
Properties of Water
Cohesion
Adhesion
High Specific Heat
High heat of vaporization
High Heat of Vaporization
 Amount of energy to convert 1g or a substance
from a liquid to a gas
 In order for water to evaporate, hydrogen
bonds must be broken.
 As water evaporates, it removes a lot of heat
with it.
High Heat of Vaporization
 Water's heat of vaporization is 540 cal/g.
 In order for water to evaporate, each gram
must GAIN 540 calories (temperature doesn’t
change --- 100oC).
 As water evaporates, it removes a lot of heat
with it (cooling effect).
Properties of Water
Cohesion
Adhesion
High Specific Heat
High heat of vaporization
Less dense as a solid
Water is Less Dense as a Solid
• Ice is less dense as a solid than as a liquid (ice
floats)
• Liquid water has hydrogen bonds that are
constantly being broken and reformed.
• Frozen water forms a crystal-like lattice
whereby molecules are set at fixed distances.
Water is Less Dense as a Solid
•Which is ice and which is water?
Water is Less Dense as a Solid
•Which is ice and which is water?
water
ice
 Water vapor forms
a kind of global
‘‘blanket” which
helps to keep the
Earth warm.
 Heat radiated from
the sun warmed
surface of the
earth is
absorbed and held
by the vapor.
Homeostasis
 Ability to maintain a steady state despite changing
conditions
 Water is important to this process because:
a. It makes a good insulator
b. It resists temperature change
c. It is a versatile solvent
d. It acts as a coolant
e. Ice protects against temperature extremes
(insulates frozen lakes)
Works Cited:
 http://wps.aw.com/bc_campbell_biology_7/25/6654/1
703570.cw/index.html